THE US State Department has barred travel by officials to the ruins of Machu Picchu, Peru's top tourist destination, citing a heightened risk of kidnapping.

A criminal organisation might be planning to abduct US tourists visiting the ruins and the surrounding Cuzco region, the US embassy in Lima said in a statement posted on its website.

''Personal travel by US embassy personnel to the Cuzco region, including Machu Picchu, has been prohibited and official travel is severely restricted as a result of this threat,'' the embassy said. ''Possible targets and methods are not known and the threat is credible at least through the end of February 2013.''

About 1.1 million tourists visited the citadel and Incan ruins in the surrounding areas last year, including 762,000 foreigners, the Tourism Observatory of Peru says.

Machu Picchu, which is about 1200 kilometres south-east of Lima, is the mainstay of Peruvian tourism, which generated $US3.3 billion in revenue last year.

The embassy said it was confident of the Peruvian government's efforts to protect tourists.

The Peruvian Trade Minister, Jose Silva, said the government considered the intelligence on which the US based its warning not to be reliable.